1. Field of the Invention
The present invention relates to side-look sonar systems, and more particularly to high resolution side-look sonar systems.
2. Description of Related Art
In a side-look sonar system, a sonar transducer transported by an underwater carrier vehicle projects pulses of acoustic energy laterally as the carrier vehicle moves relative to a target area. A beam of acoustic energy is reflected back from the target area and received by the receiving surface of a receiver transducer mounted on the side of the carrier vehicle. The side-look sonar system includes circuitry for processing the received acoustic energy to form an image of the target area on a display device. The displayed image consists of a pattern of highlights and shadows outlined to permit identification of the target area.
An increased demand for automatic target detection in side-look sonar systems has led to a need for extremely high resolution systems capable of providing precise target classification. For increased resolution, there have been developed side-look sonar systems that use a curved transducer formed by transducer segments arranged along the arc of a circle. In such a system, the curved transducer serves to focus acoustic energy reflected from the target area. Although the focused transducer may increase resolution, the acoustic energy is focused in a very small aperture.
High resolution can also be achieved in a side-look sonar system by extending the length of the transducer in a straight line. A longer transducer provides an increased receive aperture. However, practical limits on transducer length dictate that longer transducers be formed by a linear array of transducer segments. An excessive number of transducer segments undesirably complicates the system by necessitating additional processing channels. The increased size of a longer transducer also may lead to destabilization of the carrier vehicle. Moreover, acoustic energy having a curved wavefront may generate an unacceptable phase differential between individual transducer segments in the linear array.